judderbar said:

Working on the car at the moment but I made a bit of progress so far........

I traced the tube from the front canister. Under the front seats it changes to a blue plastic pipe that goes to the top connection of a check valve arrangement just under the filling cap. However between the check valve and the height of the sill it becomes a black plastic pipe and there is a quick release fitting at that position. The other two connections from the check valve arrangement are slightly lower and are black either side of the quick release fittings in that area. These black pipes must go to what I think is two separate check valves on the top of the tank.

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YellowPuntoFiat said:

So essentially, this tube should be able to allow air/fumes through freely? I presume that when I tried to pump air through the tube from the front canister it was blocked by the check valve arrangement under the filing cap (this is where I would presume the fumes should be getting evacuated from - and therefore make filing the gas tank easier). The filling cap was off during my test and no air could get through.
While it makes technical sense, not sure what the solution should be to help make pumping gas easier. Thanks for the great teardown!

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judderbar said:

I am fairly convinced this valve is not designed in any way to act as a vent when the tank is filled with petrol, other than a very small flow if you want to totally fill the tank up to the filler cap. The valve was very clean with no sign at all anything was wrong with it.

I was thinking it was illegal to vent petrol fumes when you fill up but it seems official now that is the only way to fill a Punto.

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YellowPuntoFiat said:

Thanks for the great teardown pics. It does look totally clean. And I agree that it is illegal to vent petrol fumes!

But, based on your analysis, when air is pushed through the metal pipe in the engine compartment (that connects to the charcoal filter), it should flow freely especially with the petrol tank cap is off? If it does not, that would mean there is a blockage somewhere because the petrol fumes are not really under any pressure when they flow in the other direction.

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